this one is long-winded and aint great, so sorry in advance
two men are walking through the local woods, and come acrass a HUGE hole.
They can't see the bottom so decide to try and guage the depth by throwing some gravel in.
they wait and wait and wait, but there's no sound.
next they try some pebbles, they wait again and still no sound.
next they get a rock the size of a fist, and as you''d expect no sound.
So they pick up a boulder the size of a rucksack and roll it in.....no sound.
In desperation one spots a rail tie sticking out of a bush, and they drag it across the floor, only managing to get it in.
a second later a sheep runs past and leaps, straight into the hole!
a (further) second after that, a farmer comes sprinting through the bushes, and asks, panting, "have you seen my sheep? he was tied to a rail tie!"